The field of the invention is machines for processing flat media, such as semiconductor wafers, substrates, flat panel displays, photomasks, data disks and similar articles.
In the processing of various flat media, including semiconductor wafers, it is frequently necessary to expose a surface of the flat media (referred to herein as wafers) to processing chemicals, such as various reactants, coatings, or solvents, which may be in either liquid or gas phase. For certain operations, the processing is required only on the front side of the wafer. In these operations, it is advantageous to seal the back surface of the wafer from the processing chemicals involved, simply to reduce the quantity of processing chemicals consumed. While exposing the back face of a wafer to processing chemicals may, in certain instances be irrelevant to the final semiconductor product produced, it unnecessarily increases the amount of processing chemicals used. It may also increase the amount of processing waste products, which can be costly to treat or dispose of.
In other semiconductor processing steps, it is important to seal the back face of the wafer or substrate, from the front face being processed, to avoid contamination. For example, in preparing a wafer for growth of the epitaxial layer during the manufacture of semiconductors, all pre-existing oxide must be removed from the front surface of the wafer, typically via etching with aqueous or vaporous hydrogen fluoride. The back surface must be sealed from the hydrogen fluoride to prevent contamination.
In other processes as well, it is important that a particular coating, reactant, processing chemicals, etc. not contact the back side of a wafer, because of contamination effects which can result in subsequent processing.
Existing wafer processing machines use a membrane which seals against the back side of a wafer using vacuum to prevent processing chemicals from contacting the back side. While these types of machines have been successfully used in the past, they have certain disadvantages. A substantial vacuum is required to reliably seal the membrane to the back surface of the wafer. As the wafer is drawn against the membrane, significant bending stresses develop in the wafer and can cause cracks in the wafer. In addition, the membrane in existing machines contacts a significant amount of surface area on the back surface of the wafer. As the areas contacted may be rendered unsuitable for semiconductor devices, it is advantageous to seal the back side of the wafer while touching only a minimum amount of surface area near the extreme outside edges of the wafer. Indeed, future industry standards require that machines for processing semiconductors touch semiconductor wafers only near their edges, a standard difficult or impossible to meet with existing machines.
Thus, there is a need for improved machines and methods for processing flat media, such as semiconductor wafers.
To these ends, in a first aspect of the invention, a machine for processing flat media includes a rotor having an inside and an outside ring or protrusion. A membrane extends from the inside protrusion to the outside protrusion. A stopping element on the rotor limits the deflection of the membrane and causes the membrane to seal against a small surface area on the back surface of the wafer. As a result, manufacturing efficiency is increased as more area of the wafer remains available to be processed into a semiconductor device.
In a second and separate aspect of the invention, a groove is provided in between the inside and outside protrusions, with the membrane extending across the groove. With vacuum applied to the groove, as well as to the back surface of the wafer, the contact area between the membrane and wafer is minimized, thereby increasing manufacturing efficiency.
In a third and separate aspect of the invention, the stopping element deflects a narrow annular area of the membrane into sealing contact with the back surface of the membrane. Consequently, less vacuum is required for sealing, reducing stress and the potential for cracking the wafer.
In a fourth aspect of the invention two or three of the aspects described above are combined to achieve the advantages described.
Accordingly, it is an object of the invention to provide an improved machine for processing flat media such as semiconductor wafers.